Tube bending machine including a worksupporting screw threaded, rotating mandrel



Oct. 7, 1958 R. M. STIKELEATHER 2,855,018

TUBE BENDING MACHINE INCLUDING A WORK-SUPPORTING SCREW THREADED) ROTATING MANDREL 2 Sheets-Sheet 1 Filed June 2', 1954 1953 R. M. STIKELEATHER 2,855,918

TUBE BENDING MACHINE INCLUDING A WORK-SUPPORTING SCREW THREADED, ROTATING MANDREL 2 Sheets-Sheet 2 Filed June 2, 1954 United States atent C TUBE BENDING MACHINE INCLUDING A WORK- SUPPORTING SCREW THREADED, ROTATING MANDREL Robert M. Stikeleather, Holbrook, Mass.

Application June 2, 1954, Serial No. 433,949

7 Claims. (Cl. 153-40) This invention relates to the manufacture of finned heat exchange tubes, and has as an object to bend such tubes without damage to the tubes or to the fins thereon.

Hollow heat exchange tubes having extended surface fins thereon are widely used for heating and cooling gases such as air, and are usually included in what are known as coils having rows of straight finned tubes connected at their ends by headers or return bends. For some duties, curved coils such as spiral coils, circular coils or coils formed in circular arcs are desired. Also, in some applications it is desired to have finned return bends.

A finned tube has its fins applied thereto while the tube is straight, and previous attempts to bend such tubes without damage to the fins thereon have been unsuccessful. Prior methods of bending tubes without fins theron have used stationary mandrels within the tubes for supporting the interior surfaces of the tubes during the bending, the tubes having been pulled oif the mandrels by rotation of the curved forms which bent the tubes and which were attached thereto. Such methods used with finned tubes have resulted in the fins being badly bent as a result of the force required to pull the tubes off the mandrels being applied by the bending forms to the fins.

This invention bends finned tubes without damage to the tubes or the fins thereon. In one embodiment of the invention, a revolving mandrel has a head portion and a body portion connected together by a universal joint. Both portions have ridges spiraled thereon which have outer diameters substantially the same as the inner diameter of a tube which is to be bent so that in order to place the mandrel into the tube it has to be screwed inwardly into the tube, the spiral ridges acting as screw threads. The tube to be bent has its advancing edge attached to a rotatable form which has a fin contacting trough shaped to conform with the outer edges of the circular fins on the bent tube. The mandrel is then screwed into the tube. Then the mandrel and the form are rotated. The mandrel is rotated in a direction to screw it further into the tube but is held against longitudinal movement so that it moves the tube forwardly. Thus, the force required for removing the tube from around the mandrel is provided by the revolving mandrel instead of by the bending form. The head of the mandrel follows the curvature of the tube and supports its interior surface preventing it from flattening or buckling, and thereby preventing the fins from loosening their grip on the tube.

Another object of this invention is to provide a machine which will automatically bend a finned tube to a desired shape.

This invention will now be described with reference to the annexed drawings, of which:

Fig. 1 is a fractional side elevation, partially in section, of a tube bending machine embodying this invention;

Fig. 2 is a sectional view along the lines 22 of Fig. 1, and

Fig. 3 is a diagrammatic view illustrating an embodiment of this invention in which the bending form is not 2,855,018 Patented Oct. 7, 1958 power rotated, and in which a finned tube is bent into a relatively large diameter curve.

The bending form 10 has the curved troughs 11 formed spirally therein and which are curved in circular arcs to conform with the outer edges of the spiral fins 12 on the tube 13 bent on the form, the fins being circular in outline. The form 10 which is illustrated is designed to bend a finned tube in two complete turns of a spiral. It could, of course, be designed to bend more or fewer turns or less than one turn. The illustrated form 10 could be used to bend a finned tube in less than two turns.

The form 10 has a rotary shaft 14 supported in end bearings in the supports 15. The shaft 14 has the gearing 16 attached thereto, and which is connected by the shaft 17 to the pulley 18 which is driven through the belt 19 and pulley 20 by the motor 21.

The form 10 has the tube clamp 22 attached thereto by the screws 23, the clamp having spaced-apart portions which are connected by the screw 25 which has the wingnut 26 threaded thereon for tightening the clamp against the end of a tube to be bent.

The rod 27 has a threaded portion of reduced diameter at one end which is screwed into the mandrel 28. The rod is supported at its other end by the bearing 29, and has adjacent that end, the pulley 30 attached thereto which is driven through the belt 31 and pulley 32 by the motor 21.

The mandrel 28 has a head portion 33 which has the ridges 34 formed spirally thereon, and which is connected by a conventional universal joint 35 to the body portion of the mandrel. The body portion of the mandrel has the ridges 36 spirally formed thereon adjacent the universal joint, and has the ridges 37 formed spirally thereon adjacent its other end. The ridges 34, 36 and 37 are all pitched the same and have outer diameters substantially the same as the inner diameter of the tube 13 so that to place a mandrel within the tube it has to be screwed thereinto, the ridges acting as screw threads. The grooves between the ridges 34 on the head portion 33 of the mandrel should have shallow depths for limiting the amount of metal which is forced into the grooves during the bending of the tube, and thereby limiting the thread cutting action of the ridges 34. In one mandrel used for bending a one inch diameter copper tube, eight grooves per linear inch, .005 deep were cut in the head portion'of the mandrel for forming the ridges 34.

The rolls 40 support a finned tube as it is advanced forwardly by the rotation of the mandrel, and have the rotary shafts 41 supported in hearings in the supports 42. The rolls 40 have the troughs 43 curved to conform with the curvature of the outer edges of the fins.

The finned tube tends to move upwardly as it is bent around the form 10, and to prevent such upward movement, the rolls 44 are placed over the tube rearwardly of the form 10. The rolls 44 have rotary shafts supported by bearings in the supports 46, and have troughs 47 shaped to contact the upper surfaces of the fins on the tube 13 when it is in working position.

For bending tubes to have relatively large diameters, the tube to be bent does not need to be clamped to the bending form, and the latter need not be power rotated. Referring now to Fig. 3, a tube 13 having the fins 12 thereon, has a mandrel similar to that shown by Fig. l therein, and which is rotated in the same manner as the mandrel of Fig. l. The tube is not clamped to the bending form 10 of Fig. 3, but at the start of a bending operation, is bent downwardly as by hand until it contacts the underside of the roll 51, the underside of which is below and to the right of the upperside of the form 10. The roll 52 is placed below and to the right of the roll 51 and further from the form 10 than the roll 51, and receives and supports the tube as it is bent between the form and the roll 51. As illustrated by Fig. 3, the tube is bent in a coil having a greater diameter than the diameter of the form 10. The diameter of the coil can be varied by varying the spacing of the roll 51' relative the form 10. The spacing of the roll 52 would be varied conformably with the spacing of the roll 51.

The roll 40 supports the finned tube during its movement towards the form 10. The roll 44 prevents upward movement of the tube as it is bent.

The form 10 and the rolls 40, 44, 51 and 52. have troughs shaped to conform with the outer edges of the fins as in the case of the forms and rolls of Figs. 1 and 2, but are not power rotated.

Operation of Figs. 1 and 2 In operation, at the start of a bending operation, the mandrel would be unscrewed from the rod 27, and a length of a tube to be bent would be inserted from the right, facing Fig. 1, around the rod with the outer end of the rod protruding from the outer end of the tube. The mandrel would then be screwed by hand onto the rod. The motor 21 would then be started to screw the mandrel into the tube. The tube is held against rotation so that the mandrel moves it forwardly. When the outer end of the tube reaches a position above the center of the form 10, the motor 21 is stopped, and the clamp 22 is attached to the outer end of the tube which would be free of fins for a short distance. The clamp 22 is removable from the form, and can be attached to the form anywhere around its periphery.

The motor would then be started again and screws the mandrel further into the tube, advancing it forwardly. At the same time the form 10 is rotated, and since the front end of the tube is attached to the form, the tube is bent around the form. Preferably, the form 10 is rotated at a speed just sufiicient to maintain a slight tension in the tube without, however, aiding the mandrel to any substantial extent in moving the tube forwardly. The head of the mandrel during the bending of the tube, follows its curvature, and supports the interior of the tube, preventing it from flattening or buckling, and thereby preventing the inner edges of the fins from loosening their grips on the tube. The outer edges of the fins are supported by the curved troughs of the form and are not bent or otherwise damaged during the bending of the tube since the force required to advance the tube is provided by the revolving mandrel.

When the desired curvature has been imparted to the tube, the motor 21 is stopped, and the clamp 22 is loosened. The motor can then again be started for screwing any remaining portion of the tube forwardly from around the mandrel. Since the tube would have been pre-cut to about the correct length, .there would be but a small length remaining around the mandrel.

Operation of Fig. 3

In the operation of Fig. 3, the mandrel would have been inserted within the tube and then rotated as in the case of Figs. 1 and 2 to move the tube forwardly over the form 10. When the outer end of the tube passes the center of the form 10, it would be bent downwardly as by hand and placed under the roll 51, following which the tube would continue to be advanced by the mandrel, and be bent between the form 10 and roll 51. When the bent tube has passed the roll 51, it will contact roll 52 which will support the tube as it continues to curl in a coil having a greater diameter than that of the form 10 as illustrated by Fig. 3.

While embodiments of this invention have been described for the purpose of illustration, itshould be understood that the invention is not limited to the exact apparatus and arrangement of apparatus illustrated and described, since modifications thereof may be suggested by those skilled in the art, without departure from the es sence of the invention.

What is claimed, is:

1. A machine for bending a finned tube comprising a rotary form having an outer portion shaped to conform with the outer portions of the fins on the bent portion of the tube when the tube is bent to the desired shape,

means for supporting said form for rotation, means for supporting finned tubing to be fed onto said form, a mandrel having a body portion and a head portion interconnected by a universal joint of the type which prevents relative rotation of said body and head portions, said head portion having ridges formed spirally thereon which are constructed to engage the interior of a tube to be bent by having outer diameters equal substantially to the inner diameter of the tube to be bent, means for attaching a tube to be bent to said form with said mandrel within said tube, and means for rotating the mandrel and the form.

2. A machine as claimed in claim 1 in which the body portion of the mandrel has portions with outer diameters equal substantially to the inner diameter of the tube to be bent.

3. A machine as claimed in claim 1 in which means is provided on the side of the tube opposite the side which contacts the form for preventing the rotation of the mandrel within the tube from causing movement of the tube in a direction away from the form.

4. A machine for bending a finned tube comprising a rotary form having an outer portion shaped to conform with the outer portions of the fins on the bent portion of the tube when the tube is bent to the desired shape, means for supporting said form for rotation, means for supporting finned tubing to be fed onto said form, a mandrel having a body portion and a head portion interconnected by a universal joint of the type which prevents relative rotation of said body and head portions, said body portion having ridges formed spirally thereon which are constructed to engage the interior of a tube to be bent by having outer diameters equal substantially to the inner diameter of the tube to be bent, means for attaching said tube to said form with said mandrel within said tube, and means for rotating the mandrel and form.

5. A machine as claimed in claim 4 in which the head portion'of the mandrel has ridges formed spirally thereon which have outer diameters equal substantially to the inner diameter of the tube to be bent.

6. A machine as claimed in claim 4 in which the head portion of the mandrel has portions with outer diameters equal substantially to the inner diameter of the tube to be bent.

7. A machine as claimed in claim 4 in which means is provided on the side of the tube opposite the side which contacts the form for preventing the rotation of the mandrel within the tube from causing movement of the tube in a direction away from the form.

References Cited in the file of this patent UNITED STATES PATENTS 847,094 Monnet et al. Mar. 12, 1907 1,379,168 Catucci et al. May 24, 1921 1,587,931 Wolders June 8, 1926 1,873,939 Mason et al Aug. 23, 1932 2,217,327 Zeilder Oct. 8, 1940 2,305,951 Carl Dec. 22, 1942 2,357,011 Lampe Aug. 29, 1944 FOREIGN PATENTS 1,016,617 France Apr. 27, 1955 

